452 



most Agrionidae; but it is doubtful whether this fact is really im- 

 portant. 



Some of the most interesting modifications of structure for com- 

 parison are found in the proventriculus. These were first investigated 

 by Ris ('96), who discovered interesting correlations between 

 the number of teeth and folds present and their supposed specializa- 

 tion in the different families. Conditions were simplest in the nymphs 

 of Agrionidae ; more highly specialized in the Coenagrionidae, Aesh- 

 nidae, Gomphidae, and Libellulidae. The adult structures were much 

 more complicated than those of the nymphs of the same families. 



The following table will suffice to show the important ontogenetic 

 tendencies of living forms. 



Table showing Ontogenetic Tendencies of Zygoptera 

 as compared with Anisoptera 



Egg 



Nymph 



Adult 



Anisoptera 



Zygoptera 



Anisoptera 



Zygoptera 



Anisoptera 



Zygoptera 



Eyes dichoptic 



Labium cleft 



Labial p a 1 p us 

 without fixed 

 hooks 



Median lobe 

 without setae 



Labial palpi 

 without setae 



Antennae with 

 three segments 



Eyes dichoptic 



Labium cleft 



Labial p a 1 p us 

 without fixed 

 hooks 



Median lobe 

 without setae 



Labial palpi 

 without setae 



Antennae with 

 three segments 



Eyes dichoptic 



Labium s m e- 

 times slightly 

 cleft, never 

 deeply 



Mandibles not 

 divided at tip 



Labial p a 1 p us 

 without fixed 

 hooks 



Median lobe 

 with or with- 

 out setae in 

 rows 



Labial palpi 

 with or with- 

 out setae 



Antennae with 

 3-7 segments 



Epicranial su- 

 ture traceable 



Furcae of meta- 

 sternum often 

 indistinct 



Interpleural su- 

 ture indistinct 



Eyes dichoptic 



Labium s m e- 

 times deeply 

 cleft 



Mandibles a 1 - 

 ways divided 

 at tip 



Labial p a 1 p us 

 with two fixed 

 hooks 



Median lobe 

 with or with- 

 out setae in 

 rows 



Labial palpi 

 with or with- 

 out setae 



Antennae with 

 3-7 segments 



Epicranial su- 

 ture traceable 



Furcae of meta- 

 sternum never 

 indistinct 



Interpleural su- 

 ture never in- 

 distinct 



Eyes sometimes Eyes dichoptic. 

 dichoptic, usu- 

 ally holoptic 



Labium s m e- 

 times slightly 

 cleft 



Mandibles a 1 - 

 ways divided 

 at tip 



Labial p a 1 p us 

 with one fixed 

 hook 



Median lobe 

 with setae, but 

 not in rows 



Labial palpi 

 without setae 



Antennae with 

 4-7 segments 



Epicranial su- 

 ture traceable 

 with difficulty 



Furcae of meta- 

 sternum con- 

 cealed 



Labium usually 

 deeply cleft. 



Mandibles a 1 - 

 ways divided 

 at tip. 



Labial palpus 

 with one fixed 

 hook. 



Median lobe 

 with setae, but 

 not in rows. 



Labial palpi 

 without setae. 



Antennae with 

 4-7 segments. 



Epicranial su- 

 ture traceable 

 with difficulty. 



Furcae of meta- 



sternum con- 

 cealed. 





